Gut microbiota signatures in mild cognitive impairment: a scoping review of microbial taxa and clinical implications

Abstract

Objective To identify systematically the typical gut microbiota in mild cognitive impairment patients and its association in disease progression. Systematically identify microbial taxa consistently associated with Mild Cognitive Impairment. Design A scoping review was performed according to the guidelines of the Joanna Briggs Institute using CoCoPop design. Study selection Several studies about gut microbiota sequencing in mild cognitive impairment diagnosed patients compared against healthy controls. Methods Searches in PubMed, Embase, Scopus, and Web of Science using MeSH and DeCS terms, were performed up to December 2025. Two reviewers independently screened titles and abstracts. Then, the full texts were reviewed to select documents to be included. When there were disagreements in papers selection, those were resolved after discussions among the reviewers. Relevant data information from selected publications was extracted, and a descriptive analysis was made. Results The documents do not show drastic changes in the alpha or beta diversity of the microbiota, but they do identify consistent alterations in the relative abundance of specific taxa that allow patients with MCI to be distinguished from healthy controls. Among the most relevant findings is the decrease in SCFA-producing genera, such as Ruminococcus and Lachnospira, whose reduction is directly associated with the deterioration of key brain functions, including synaptic processes and neuronal oxidative metabolism. On the other hand, there is an increase in proinflammatory taxa such as Bacteroides, a pattern that is similar to that observed in patients with Alzheimer’s disease, although generally less pronounced. Conclusion The results highlight that alterations in the abundance of specific bacteria, characterized by the loss of protective taxa and an increase in proinflammatory bacteria, serve as early biomarkers for detecting and predicting Mild Cognitive Impairment (MCI). This pattern of proinflammatory dysbiosis can be identified even in preclinical stages, and it has been proposed as a potential noninvasive tool for early diagnosis and therapeutic intervention before dementia progresses.